Throughout the year when I am writing these articles, I try to avoid repeating information because I prefer to keep offering you information that is different and new. Occasionally I need to make exceptions. This happens when there is something happening that poses a potential threat to plants that might be growing in your landscape.
The box tree moth is an insect that certainly fits this description. This insect is causing major damage to most varieties of boxwood shrubs. Boxwoods are the most common evergreen shrubs used by most landscapers.
This insect has spread very quickly through sections of Southwest Ohio. It was first detected in Loveland on the borders of Hamilton and Clermont counties in 2023. Last year, 2025, it was spreading and showing up in many more communities. These were mostly on the east side of I-71.
Most people don’t see the damage until it’s too late. The insects are hard to detect. There are not any insecticides available you can spray to prevent the damage. I want to help you prepare a strategy so you can be ready to protect your boxwoods.
First you need to understand the life cycle of this insect. The insect when it is a moth is not the problem. These moths lay eggs in the boxwood shrubs. Then the eggs will hatch as caterpillars. This is when the damage is done. They are lime green with black stripes. They are very well-camouflaged and big eaters. This is why you do not see them until the damage is pretty severe.
Box tree moth.
Then they form cocoons and then hatch as moths again. This life cycle occurs quickly, leaving the potential for 3-4 generations of this insect in one season. Once you have them you must continually monitor your plants on a weekly basis.
They become active when the weather starts to warm. You need to start monitoring your boxwoods around the middle of May. This would be especially true if you had them last year or they were present in your neighborhood.
You can start the monitoring process by getting a trap for catching the moths. Garden stores are starting to sell them. You will hang this trap in the vicinity of your boxwoods. They are baited with a lure to attract the moth. The trap will serve two purposes.
The first is hopefully catching the moths before they can lay their eggs. However, there is no way to tell if they laid eggs or not. The second purpose the trap serves is it becomes your alarm that it is time to start monitoring your boxwoods for the worms. You need to pull the branches apart gently with your hand to look inside of the plant. The eggs are usually deep in the plant, and the feeding starts on the inside.
When you see the first worm it is time to start treating the plants with an insecticide. In the short time we have been combating these insects, products containing Spinosad have proven to be the most effective. The Spinosad works as it comes in contact with the caterpillars. It also has a residual effect when it is on the foliage, allowing the caterpillars to ingest it.
This Spinosad will only remain on the foliage for 3-7 days. The strategy with spraying is to spray once a week for three weeks when you see the moths and/or caterpillars. After a three-week spraying cycle, you will need to repeat the spraying 3-4 weeks later. This is when a new generation could hatch. You will need to continue this as long as it’s warm into Fall.
It is understandable if this is a challenge you do not want to accept. If you choose not to spray you will have to consider replacing your boxwoods with alternative shrubs.
This article originally appeared on Cincinnati Enquirer: This insect is killing your boxwood shrubs. Here’s how to protect them
